Superheat controller

Claim 1

A refrigerant flow control system for a refrigeration system of the type having a compressor including a discharge and suction conduit, a condenser, an electro-mechanical expansion means for regulating refrigerant flow in said system and an evaporator for receiving liquid phase refrigerant at an inlet and providing gaseous phase refrigerant at an outlet; means controlling said expansion means in accordance with the superheat condition at said suction conduit by regulating the admission of liquid phase refrigerant to said evaporator comprising: a sensing member including a cavity; a differential pressure responsive element arranged to divide said cavity into a first and second chamber with at least a portion of said sensing member including said second chamber being in thermal contact with said suction line; a fluid in said second chamber having characteristics approaching or identical with those of the refrigerant employed in said system; a conduit introducing gaseous phase refrigerant at suction line pressure to said first chamber so that said differential pressure responsive element is subjected on one side to saturation pressure of said fluid in said second chamber under influence of said suction line temperature and on the other side to refrigerant in said first chamber at suction line fluid pressure; a differential pressure sensing means arranged on said differential pressure responsive element for sensing the difference in pressure between said first chamber and second chamber, said differential pressure sensing means including strain sensing resistive elements whose resistance varies as a function of pressure differential between said chambers; a signal means for producing an electrical signal from the action of the said differential pressure sensing element for controlling operation of said electro-mechanical expansion means; and control means for causing said electric signal to activate said electro-mechanical expansion means for controlling the superheat condition of said gaseous phase refrigerant in said suction conduit in accordance with the pressure differential between said first and second chambers.